The invention firstly relates to leakage devices, and especially to devices for detecting the puncturing of tyres of motor vehicle wheels and more precisely to calculating the leakage rate from these tyres.
The detection devices may be integrated into computers in the passenger compartment or more specifically into TPMS (Tyre Pressure Measurement System) modules.
A TPMS module collects the information about the pressure P and temperature T of the gas contained in a tyre by means of sensors and a radio transmitter, these generally being fastened to the rim of the wheel. A radio receiver placed in the module periodically receives a data packet representative of the pressure and temperature.
The period of collection of the data packets from each wheel is, in principle, the inverse of the theoretical frequency with which the data packets are transmitted by the transmitters, which is determined by the passenger compartment computer according to the operating state of the vehicle (at rest or running).
To detect a leak, its leakage rate may be calculated from the change in the pressure, from one data packet to another, at the above theoretical frequency, that is to say the leakage rate is calculated from the pressure difference recorded over the theoretical time.
However, this detection is not ideal.
Firstly, the temperature of the rim, and therefore of the gas contained in the tyre, may vary substantially, for example during a braking operation. This causes a change in the pressure and a change in the calculated leakage rate that may be interpreted wrongly as a leak. This is because the thermal compensation, even if it is applied, has no immediate effect given the long response time of a temperature sensor, which is longer than that of a pressure sensor.
Secondly, the time between two data packets may not be constant:                1) it may be intentionally reduced, for example if the tyre pressure monitoring requires to be increased, in which case the calculated leakage rate decreases with time between two data packets;        2) it may unintentionally increase in the event of a data packet being lost, caused by a poor radio link. The calculated leakage rate may then double, triple, etc., unbeknown to the TPM module, which therefore cannot apply the slightest correction.        
Mathematical algorithms for smoothing temperature and pressure data in order to attenuate the effects of these sources of error are known. However, this solution does not prevent a delay in detecting an actual puncture, or an adventitious detection. This may be prejudicial to the safety of the driver and the passengers of the vehicle.